The present invention relates to the field of heat engine control.
More specifically, its subject is a method for estimating the torque of a heat engine in a vehicle hybrid transmission comprising at least a heat engine and an electric machine together or separately supplying a heat engine torque and an electric torque intended for the wheels of the vehicle.
This method can be applied to any heat engine or hybrid powertrain having two rotating shafts (or pinions) that need to be synchronized in order to engage a transmission ratio.
Torque control of a heat engine in a hybrid or non-hybrid vehicle is of capital importance in improving the overall performance of the vehicle and the drivability thereof.
When the gearbox associated with the engine is a parallel shafts gearbox comprising at least a primary shaft connected to a power source and a secondary shaft driven by the primary shaft in order to transmit the motive torque to the wheels, it requires good control over the (heat engine and/or electric) torque in order to avoid potential jerkiness in the torque curve as torque is reapplied after the changes in gear ratio. Control over the motive torque during the changes in gear ratio is of particular importance in certain hybrid architectures in which the synchronizing of the two gearbox shafts, prior to engaging a gear ratio, is assigned to the heat engine.
However, the measurement of the torque of the heat engine is not directly available in a vehicle moving along. One means for obtaining its value is to estimate (reconstruct) it indirectly from measurements of the angular rotational speed of the crankshaft.
Publication FR 2 681 425 discloses a method for measuring the torque of an internal combustion heat engine using the signal produced by a sensor associated with the engine flywheel ring gear. This method makes it possible to calculate the mean torque produced by each combustion of the gaseous mixture in each cylinder of the engine. The calculated values can be used to continuously improve engine operation and monitor defects thereof. The engine management computer is capable of adapting to the empirical measurements taken from the flywheel ring gear. Continuous improvement of combustion performance is performed by loop control of the combustion parameters, this all assuming good knowledge of the dynamics of the combustion systems and the response times thereof.
This method is somewhat unsatisfactory in complex environments such as hybrid architectures, because of the combined effects of the inertias and frictions within the powertrain. Each motive power source, heat engine and electric machine, actually has its own dynamics and its own level of response specific to the control instructions.
When the two shafts (pinions) that are to be coupled are synchronized by way of the heat engine, the latter needs moreover to meet the driver's demand for torque. The control system therefore demands very accurate information regarding the instantaneous value of the heat engine torque. It is notably necessary for the discrepancy in speed between the shafts that are to be synchronized to converge very quickly to a range of 30 revolutions per minute in order for the gearshift to be acceptable, with a speed differential that is as small as possible. The phase that follows on from the coupling of the two shafts (reapplication of torque) also needs to be transparent, which means to say to take place with the least possible amount of jerkiness.